The Shrine maiden is not reimu, she is Training on Mt. Haku shrine maiden, post #103368

This girl was created by ZUN, the girl with blue hair and pink dress was created by ZUN, she is one of the two girls from Oekaki images
https://en.touhouwiki.net/wiki/Miscellaneous_illustrations_by_ZUN#Oekaki_images

She is seen playing a board game that I don't know, I think he is playing reversi, but, it could also be that he is playing Gomoku
https://en.wikipedia.org/wiki/Gomoku